The field of the invention is synthetic resins from polyhydric alcohol-polycarboxylic acid reaction products. The invention is particularly related to a process for the manufacture of low pilling-effect polyester fiber products.
The state of the art of the present invention may be ascertained by reference to the Kirk-Othmer "Encyclopedia of Chemical Technology", Vol. 16 (1968), pages 143-159, under the section entitled "Polyester Fibers"; U.S. Pat. No. 2,465,319 which shows the preparation of polyethylene terephthalate; U.S. Pat. No. 3,391,123 of Stedley which issued July 2, 1968, and shows the state of the art of improving the pilling effect of polyethylene terephthalate textile fibers; West German Patents 1,148,520 and 1,290,516 of Kretsch-Hothum et al which shows an improvement in the dyeability of polyesters by the addition of cyclobutanedicarboxylic acid to the melt-polymerization; and USSR Patent 322,985 which issued May 15, 1972 and shows the preparation of the .alpha.-truxillic acid preferred for use in the present invention, the disclosures of which are incorporated herein.
Because of the large number of outstanding properties such as high melting point, chemical corrosion resistance, stability with respect to heat, hot water and light, and also on account of their mechanical properties, threads and fibers made of polyethylene terephthalate have achieved large significance in the garment industry.
However, polyester fibers also do suffer from drawbacks. One of these is the so-called pilling effect, which is caused by fibers being pulled out of the cloth during wear and then twisting into small spheres firmly anchored to the cloth. The fabric surface thereby assumes an unpleasant appearance and decreases the quality of the particular item.
Many attempts have been undertaken to remedy this drawback in polyester by various steps.
The most frequently used method consists in reducing the molecular weight of the polyester and in correspondingly reduced specific viscosities (hereafter abbreviated by RSV) of about 0.35 - 0.45 dl/g (deciliters per gram as measured at a concentration of 0.23 g in 100 ml phenol and tetrachloroethane (60 : 40) at 25.degree. C similar to German Industrial Standard DIN 53728 page 3), and therewith obtaining a reduction in thread strength, as disclosed in Japanese Patent 24,932 which issued in 1965. However, extrusion or melt spinning of such a material causes appreciable difficulties on account of the low viscosity of the melt.
Another approach consists in preparing polyesters containing such compounds as alcohols or carboxylic acids with three or more functional groups, for instance glycerine, pentaerythrite or trimesinic acid as disclosed in German Published Application 1,928,436.
Partially branched polyesters are obtained in the process. The drawback of this method arises from the very precise dosage required of the branching components, which may not always be ensured in industrial practice. Therefore, there is danger of polyester reticulation which may cause failure of the entire polycondensing system.
Again, many attempts have been undertaken to destructively test polyester fibers and fabrics made therefrom by treating them at high temperatures with water, soda, ammonium, hydrazine, carboxylic acids or alcohols as disclosed in Czech Patent 108,680; Dutch Patent 91,330; French Patent 1,551,050; Japanese Patent 7,122,174; and German Published Application 1,024,482. It has been found, however, that such decomposition presents difficulties relating to control and reproducibility. In many cases, attempts were undertaken to create weak spots in the molecule by incorporating chain links with hetero-atoms, especially silicon, as disclosed in U.S. Pat. No. 3,335,211 and German Published application 1,273,123; boron as disclosed in U.S. Pat. No. 3,335,211 and German Published Application 1,469,127, or aluminum as disclosed in German Published Application 1,545,039, which may also cause branching or reticulation, with hydrolytic dissociation being subsequently feasible at these weak spots. Again, difficulties are encountered regarding reproducibility of these products. Furthermore, the operation must be entirely free from water up to the time of the desired hydrolytic decomposition or reduction. It is generally known that special difficulties are caused by the latter requirement.
As clearly shown above, all the known methods suffer from a series of drawbacks.